Poly (lactic acid) fiber

ABSTRACT

A poly(lactic acid) fiber has a strength at 90° C. of equal to or more than 0.8 cN/dtex and exhibits significantly satisfactory mechanical properties at high temperatures as compared with conventional poly(lactic acid) fibers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to poly(lactic acid) fibers havingsatisfactory mechanical properties at high temperatures.

2. Description of the Related Art

Strong demands have been made on polymer materials that are decomposedin the environment and are thereby environmentally friendly. As possiblecandidates therefor, aliphatic polyesters and other polymers have beeninvestigated, developed and been launched. Among them, polymers that aredecomposed by microorganisms, i.e., biodegradable polymers have become afocus of attention.

Most of conventional polymers are made from petroleum resources.However, the petroleum resources are limited and will probably beexhausted in the future. In addition, the petroleum resources arederived from hydrocarbons in fossils in a geologic age and have beenaccumulated in the ground, and heavy consumption and burning of thepetroleum resources invites emission of carbon dioxide into theatmosphere to thereby cause global warming. If polymers can besynthesized from vegetable resources that take in carbon dioxide fromthe atmosphere for their growth, such vegetable-origin polymers areexpected to decrease carbon dioxide in the atmosphere as a result of“carbon dioxide circulation” and to solve problems of the exhaustion ofthe petroleum resources. Polymers derived from the vegetable resources,i.e., biomass-derived polymers have therefore received attention.

Such biomass-derived biodegradable polymers receive great attention andare expected to be an alternative to conventional polymers derived fromthe petroleum resources. However, such biomass-derived biodegradablepolymers generally have insufficient mechanical properties and heatresistance and require high cost for their production. The mostnoteworthy polymer as a biomass-derived biodegradable polymer that cansolve these problems is poly(lactic acid). The poly(lactic acid) is apolymer derived from lactic acid, which lactic acid can be obtained byfermenting starch extracted from vegetable. The poly(lactic acid) hasthe best balance in mechanical properties, heat resistance and costamong such biomass-derived biodegradable polymers. Fibers using thepoly(lactic acid) have-been developed at a feverish pace.

However, even the most promising poly(lactic acid) has somedisadvantages as compared with the conventional polymers. One of seriousdisadvantages is insufficient mechanical properties at hightemperatures. The phrase “insufficient mechanical properties at hightemperatures” used herein means that the poly(lactic acid) rapidlybecomes soft at temperatures exceeding 60° C., i.e., the glasstransition temperature (T_(g)) of the poly(lactic acid). With referenceto FIG. 3, when a conventional poly(lactic acid) fiber is subjected to atensile test at different temperatures, the poly(lactic acid) fiberrapidly becomes soft at temperatures in the vicinity of 70° C. or higherand becomes nearly fluid and exhibits markedly deteriorated dimensionalstability at 90° C. In contrast, a fiber of nylon 6 (polyamide 6), aconventional polymer, does not become soft so rapidly and exhibitssufficient mechanical properties even at 90° C.

The poly(lactic acid) fiber has insufficient mechanical properties suchas strength and creep resistance at high temperatures as mentioned aboveand actually invites problems. For example, when the poly(lactic acid)fiber is used as the warp of woven fabrics, the warp is sized and driedwith hot air for better condensing and better weaving. However, upon hotair drying, the warp poly(lactic acid) fiber elongates by action oftension applied to stretch the warp taut. When products made from thepoly(lactic acid) fiber are used in a high-temperature atmosphere, theyhave some problems in their durability. For example, Kogyo Zairyo(Industrial Materials), No. 6, p82 (2001) mentions that the insidetemperature of cars in summer reaches 72° C. on the surface of a frontseat and 80° C. on the surface of an upper side of a rear seat. When thepoly(lactic acid) fiber is used as a fabric for car seats, the resultingcar seats have insufficient durability, since the surface temperaturesof car seats exceed T_(g) of the material poly(lactic acid).

These problems significantly limit the applications of the poly(lacticacid) fiber. Accordingly, demands have been made on poly(lactic acid)fibers having improved mechanical properties at high temperatures.

Japanese Unexamined Patent Application Publication No. 2000-248426discloses a high-strength yarn obtained by multistage drawing of apoly(lactic acid) undrawn yarn formed by low-velocity spinning. However,the results in further testing made by the present inventors show thateven a high-strength yarn having a strength of 7 cN/dtex obtained bymultistage drawing does not have practically satisfactory mechanicalproperties at high temperatures (Comparative Example 1). However,differences in mechanical properties at high temperatures cannot beexplained by strength at room temperature alone, since such ahigh-strength poly(lactic acid) yarn has insufficient mechanicalproperties at high temperatures, but a high-strength poly(ethyleneterephthalate) yarn has satisfactory mechanical properties at hightemperatures. Thus, insufficient mechanical properties at hightemperatures are unique to the poly(lactic acid) fibers.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide apoly(lactic acid) fiber having satisfactory mechanical properties athigh temperatures.

Specifically, the present invention provides, in an aspect, apoly(lactic acid) fiber having a strength at 90° C. of equal to or morethan 0.8 cN/dtex.

The present invention further provides, in another aspect, process forproducing a poly(lactic acid) fiber. The process includes the step ofdrawing a poly(lactic acid) undrawn yarn at such a drawn ratio (DR) asto satisfy the following condition:0.85+(EL/100)≦DR≦2.0+(EL/100)wherein EL is the elongation (%) of the undrawn yarn.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates plots of strength versus elongation at roomtemperature and at 90° C. on Example 1 and Comparative. Example 1 (aconventional high strength poly(lactic acid) fiber);

FIG. 2 illustrates plots of strength versus elongation at 90° C. onExamples 2 and 10 and Combative Example 3 (a conventional poly(lacticacid) fiber);

FIG. 3 illustrates plots of strength versus elongation on theconventional poly(lactic acid) fiber (Comparative Example 3) and a nylon6 fiber;

FIG. 4 illustrates helical structures of poly(lactic acid) molecularchains;

FIG. 5 shows solid state NMR spectra of high strength poly(lactic acid)fibers according to the present invention (Examples 1 and 2) and theconventional high-strength poly(lactic acid) fiber (Comparative Example1);

FIG. 6 illustrates peak resolution of the solid state NMR spectra;

FIG. 7 illustrates a wide angle X-ray diffraction pattern of Example 1;

FIG. 8 is a transmission electron microscopic image showing the state ofblend in a fiber according to Example 10;

FIG. 9 schematically illustrates a spinning machine used in Examples 1to 12 and 19 to 21 and Comparative Examples 2, 3, 8 to 14 and 17;

FIG. 10 is schematically illustrates a drawing machine used in Examples1 to 12 and 19 to 21 and Comparative Examples 2, 3, and 8 to 14;

FIG. 11 schematically illustrates a draw false-twist texturing machineused in Examples 13 to 17 and Comparative Examples 15 to 17;

FIG. 12 schematically illustrates a spinning machine used in ComparativeExamples 5 and 6;

FIG. 13 schematically illustrates a spinning machine used in ComparativeExample 7;

FIG. 14 illustrates a plot of strength versus elongation on apoly(lactic acid) crimped yarn (Example 14); and

FIG. 15 illustrates a plot of strength versus elongation on aconventional poly(lactic acid) false-twist yarn (Comparative Example15).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term “poly(lactic acid)” as used herein means and includes polymersobtained by polymerization of lactic acid. Such poly(lactic acid)include poly(L-lactic acid) and poly(D-lactic acid), and the opticalpurity thereof is preferably equal to or more than 90% for highermelting point. The term “poly(L-lactic acid) (PLLA)” as used hereinmeans a poly(lactic acid) having an optical purity in terms of L-lacticacid of equal to or more than 90%, and the term “poly(D-lactic acid)(PDLA)” means a poly(lactic acid) having an optical purity in terms ofD-lactic acid of equal to or more than 90%. The poly(lactic acid) may bea copolymer of lactic acid with another comonomer or may furthercomprise the other polymers than poly(lactic acid), as well aslubricants, flame retarders, antistatic agents and other additiveswithin ranges not deteriorating the properties of the poly(lactic acid).Specifically, the poly(lactic acid) should preferably further comprise alubricant when the resulting poly(lactic acid) fiber is used inapplications which require wear resistance, since the poly(lactic acid)fiber has low wear resistance. As such lubricants, carboxylic amides arepreferred, of which carboxylic amides having a high melting point aretypically preferred. Such carboxylic amides having a high melting pointare resistant to thermal decomposition and bleed out during processsteps from spinning to fabric processing. From the viewpoints of biomassutilization and biodegradability, the poly(lactic acid) preferablycomprises a lactic acid monomer as a monomer component in an amount ofequal to or more than 50% by weight, preferably equal to or more than75% by weight, and more preferably equal to or more than 96% by weight.The poly(lactic acid) preferably has a weight average molecular weightof 50000 to 500000 for well-balanced mechanical properties andstabilizing yarn-producing.

Such poly(lactic acid) for use in the present invention can be obtained,for example, according to processes described in PCT InternationalPublications No. WO94/07949 WO94/07949 and No. WO98/50611, JapaneseUnexamined Patent Application Publications No. 2001-261797, No.2001-64375, No. 2001-64400, and No. 2001-122954.

To improve mechanical properties at high temperatures to thereby avoidelongation of yarn during sizing and drying procedures and to improvedurability of the products in a high-temperature atmosphere, thepoly(lactic acid) fiber must have a strength at 90° C. of equal to ormore than 0.8 cN/dtex. The strength at 90° C. is preferably equal to ormore than 1.0 cN/dtex, more preferably equal to or more than 1.3cN/dtex, and typically preferably equal to or more than 1.5 cN/dtex.

The poly(lactic acid) fiber of the present invention preferably has acreep rate at 90° C. of less than or equal to 15%. The creep rate at 90°C. can be determined by subjecting a sample fiber to a tensile test at90° C., plotting strength against elongation, and reading the elongationat a stress of 0.7 cN/dtex. Such a poly(lactic acid) fiber having acreep rate at 90° C. of less than or equal to 15% can have furtherimproved dimensional stability at high temperatures. The creep rate at90° C. is more preferably less than or equal to 10% and furtherpreferably less than or equal to 6%.

If the poly(lactic acid) fiber exhibits large unevenness of yarn, theresulting fibrous products have deteriorated appearance quality andfrequently invite fluff, slack and other defects. When the poly(lacticacid) fiber is used as a multifilament, it is generally subjected toaftertreatment for dying or for imparting functional substances. If thepoly(lactic acid) fiber exhibits large unevenness of yarn in this case,it tends to cause dyeing speck and other unevenness in processing. Toavoid these problems, an poly(lactic acid) yarn constituting thepoly(lactic acid) fiber of the present invention has Uster unevenness (U%) of preferably less than or equal to 1.5%, and more preferably lessthan or equal to 1.2%. The Uster unevenness is an index of unevenness inyarn thickness of a yarn.

To further improve processability during process steps for manufactureof fibrous articles and to further improve the mechanical properties ofthe products, the poly(lactic acid) fiber of the present invention has astrength at 25° C. of preferably 2 cN/dtex, more preferably 3.5 cN/dtex,and further preferably equal to or more than 5 cN/dtex.

To improve processability during process steps for manufacture offibrous articles, the poly(lactic acid) fiber of the present inventionpreferably has an elongation at 25° C. of from 15% to 70%.

The boiling water shrinkage of the poly(lactic acid) fiber is preferablyfrom 0% to 20%, and more preferably from 2% to 10% to improvedimensional stability of the fiber and the resulting fibrous articles.

Poly(lactic acid) fibers herein are not specifically limited as long asthey have the satisfactory physical properties as mentioned above.However, more preferred embodiments of the present invention are apoly(lactic acid) fiber having a specific fiber structure and a polymerblend fiber comprising a blend of a poly(lactic acid) and an aromaticpolyester.

At first, the poly(lactic acid) fiber having a specific structure willbe illustrated in detail below. This type of poly(lactic acid) fibercomprises a poly(D- or L-lactic acid) molecular chain constituting a 3₁helical structure by itself. The 3₁ helical structure will beillustrated in detail below.

The structure of molecular chain in a regular poly(lactic acid) fiberwill be described. The poly(lactic acid) fiber is usually of an alphacrystal form in which the molecular chain has a 10₃ helical structure asdescribed in J. Biopolym., vol. 6, 299 (1968). With reference to FIG. 4,the 10₃ helical structure means a helical structure of which helixrotates three times per ten monomer units. In contrast, another type ofpoly(lactic acid) fiber comprises a beta crystal different from thealpha crystal, as described in Macromolecules, vol. 23, 642 (1990). Thistype of poly(lactic acid) fiber is obtained in the following manner. Anultrahigh molecular weight poly(lactic acid) having a viscosity averagemolecular weight of 56×10⁴ to 100×10⁴ is dissolved in achloroform-toluene solvent mixture, the resulting solution is subjectedto solution spinning at a spinning speed of 1 to 7 m/min to yieldfibers, and the fibers are drawn at an ultrahigh temperature of 204° C.higher than the melting point at an ultrahigh draw ratio of 12 to 19 ata drawing speed of less than or equal to 1.2 m/min. The beta crystal hasa 31 helical structure (FIG. 4) of which helix rotates once per threemonomer units (Macromolecules, vol. 23, 642 (1990)). From anotherviewpoint, the 3₁ helical structure is a helical structure of whichhelix rotates three times per nine monomer units and is a stressedcrystal obtained by stretching the 10₃ helical structure to some extent.

Based on solid state ¹³C-NMR analyses, the present inventors have foundthat conventional poly(lactic acid) fibers only show a peak in thevicinity of 170.2 ppm corresponding to the 10₃ helical structure but thepoly(lactic acid) fiber of the present invention shows a peak at 171.6ppm, lower than 170.2 ppm, as shown in FIG. 5. The results demonstratethat the poly(lactic acid) fiber of the invention has a helicalstructure significantly different in configuration from the 10₃ helicalstructure of the conventional poly(lactic acid) fibers. It has beenverified that the helical structure in question is a 3₁ helicalstructure, since a pattern analogous to that of beta crystal is observedin wide angle X-ray diffractometry (WAXD) (FIG. 7). Specifically, thepresent inventors have found that a peak observed in the vicinity of171.6 ppm in solid state ¹³C-NMR analysis means that the 3₁ helicalstructure is formed.

The poly(lactic acid) fiber of the present invention has only tocomprise the 3₁ helical structure at least partially. The integratedintensity of a peak corresponding to the 3₁ helical structure (3₁ ratio)occupies preferably equal to or more than 12% of that of peaks observedat 165 to 175 ppm in a solid state ¹³C-NMR spectrum. The resultingpoly(lactic acid) fiber can have a strength at 90° C. of equal to ormore than 1.0 cN/dtex. The 3₁ helical structure is not necessarilycrystallized, but is preferably crystallized to such an extent as to beobserved in WAXD images as in FIG. 7. By this configuration, theresulting poly(lactic acid) fiber can have a strength at 90° C. of equalto or more than 1.5 cN/dtex in some case.

The phrase “a L- or D-poly(lactic acid) molecular chain constitutes a 3₁helical structure by itself” means a state in which the PLLA moiety orPDLA moiety constitutes the 3₁ helical structure independently and isdistinguished from the state in which a pair of the PLLA moiety and PDLAmoiety constitutes a 3₁ helical structure as in a “stereocomplex”.

The aforementioned poly(lactic acid) fiber obtained by drawing thesolution-spun fiber at an ultrahigh draw ratio of 12 to 19 at anultrahigh temperature of 204° C. higher than its melting point describedin Macromolecules, vol. 23, 642 (1990) has U % of equal to or more than10% and is not practically used as a yarn. This is for the followingreasons. Specifically, in this technique, the undrawn yarn is spun froma solution, but the resulting undrawn yarn exhibits unevenness of yarn,since the solvent usually extracts from the surface of the fiber duringsuch solution spinning, and depressions and protrusions occur on thesurface of the fiber to thereby cause unevenness of yarn. The undrawnyarn is then drawn at an ultrahigh temperature higher than its meltingpoint, but the constitutive yarn partially melts during drawing processand cannot be drawn homogeneously to thereby further cause unevenness ofyarn. In addition, the yarn is drawn at such an ultrahigh draw ratio ofequal to or more than 12 and cannot be drawn stably to thereby furtherinvite unevenness of yarn. Additionally, the spinning speed and drawingspeed are excessively low, and the fiber becomes susceptible todisturbance during drawing, thus further increasing unevenness of yarn.

Processes for producing the poly(lactic acid) fiber of the presentinvention include, but are not specifically limited to, a process inwhich an oriented and crystallized poly(lactic acid) fiber is drawn at ahigh draw ratio as described below.

In the process just mentioned above, setting of the draw ratio (DR) istypically important, and DR must satisfy the following condition:0.85+(EL/100)≦DR≦2.0+(EL/100)wherein EL is the elongation (%) of the undrawn yarn.

A conventional poly(lactic acid) fiber for use in apparel has a drawratio of less than or equal to [0.75+(EL/100)] (Comparative Example 3).Even a conventional poly(lactic acid) fiber for industrial use has adraw ratio of much lower than that in the poly(lactic acid) fiber of thepresent invention. For example, the draw ratio is less than or equal to[0.75+(EL/100)] at the first drawing stage in the process described inJapanese Unexamined Patent Application Publication No. 2000-248426.

In the process of the present invention, the poly(lactic acid) fiber isproduced by drawing at a much higher draw ratio than in conventionalequivalents, and the fiber structure of the material undrawn yarn isonce destructed and reconstructed to yield a specific fiber structure tothereby improve the mechanical properties at high temperatures. In thisconnection, Japanese Unexamined Patent Application Publication No.2001-226821 describes a spinning process in which a yarn is drawn andheat-treated in a heating tube in the spinning line. The draw ratio inthis process can be estimated by determining a yarn speed profile withan on-line yarn speed meter along the spinning line and is found to benot higher than that in fibers for use in apparel, by taking apoly(ethylene terephthalate) fiber as an example. This spinning processcannot therefore produce the poly(lactic acid) fiber having satisfactorymechanical properties at high temperatures of the present invention. Bysetting the draw ratio DR less than or equal to [2.0+(EL/100)], thefiber can be prevented from excessive deformation to thereby avoid yarnbreakage and unevenness of yarn significantly. The draw ratio DR shouldmore preferably satisfy the following condition:0.95+(EL/100)≦DR≦1.5+(EL/100), and further preferably satisfy thefollowing condition: 1.1+(EL/100)≦DR≦1.4+(EL/100)

In the process of the present invention, a second important factor isthe orientation and crystallization of the undrawn yarn. The undrawnyarn for use in the present invention preferably is oriented andcrystallized so as to have a crystalline size in the (200) plane ofequal to or more than 6 nm. By this configuration, yarn breakage anduneven yarn can be prevented even when the undrawn yarn is drawn at sucha high draw ratio as mentioned above. The crystalline size of theundrawn yarn is more preferably equal to or more than 7 nm, and furtherpreferably equal to or more than 9 nm. In addition, the undrawn yarnpreferably has a degree of orientation of equal to or more than 0.90. Bythis configuration, the molecular chain can stably be drawn from thecrystalline to thereby enable the undrawn yarn to be drawn out stablyeven at a high draw ratio.

To yield such a crystallized undrawn yarn, poly(lactic acid) ispreferably subjected to melt spinning at a spinning speed of equal to ormore than 4000 m/min, and more preferably equal to or more than 5000m/min.

The drawing temperature is preferably equal to or higher than 85° C.,and more preferably equal to or higher than 130° C. At such a drawingtemperature, the molecular chain can stably be drawn from thecrystalline to thereby enable the undrawn yarn to be drawn stably evenat a high draw ratio. In contrast, the drawing temperature is preferablylower than or equal to 160° C., since poly(lactic acid) has a meltingpoint of around 170° C. under normal conditions. If an undrawn yarnwhich has not been oriented and crystallized is used, the undrawn yarnfrequently becomes soft or spontaneously elongates on a preheat rollerat a drawing temperature of equal to or higher than 130° C. to therebycause instability of yarn running and yarn winding to a roller, and theprocess steps become unstable. By using the oriented and crystallizedpoly(lactic acid) fiber as the undrawn yarn, these problems can besolved.

The temperature of heat treatment is preferably equal to or higher than120° C. and more preferably equal to or higher than 140° C. By treatingat such a temperature, the resulting drawn yarn can have a stabilizedfiber structure and have sufficient strength and a low boiling watershrinkage. In addition, such a high temperature heat treatment canstabilize drawing and heat treatment procedures to thereby prevent yarnbreakage and uneven yarn. However, the heat treatment should preferablybe performed at a temperature lower than or equal to 165° C., sincepoly(lactic acid) has a melting point around 170° C. under normalconditions.

When an undrawn yarn which has not sufficiently been oriented andcrystallized, i.e., which has a crystalline size in the (200) plane ofless than or equal to 6 nm is used, the drawing temperature plays atypically important role is preferably set at equal to or higher than110° C. and more preferably equal to or higher than 130° C. By drawingat such a temperature, the undrawn yarn is oriented and sufficientlycrystallized by preheating prior to drawing and can be drawnsatisfactorily homogeneously, as in the oriented and crystallizedundrawn yarn.

The term “undrawn yarn” as used herein means fibers that can be stablydrawn under the aforementioned drawing conditions. Consequently, theundrawn yarn preferably has an elongation of equal to or more than 25%.For better productivity, the undrawn yarn is preferably a yarn which hasnot been subjected to other treatments after spinning. To prevent unevenyarn, the undrawn yarn preferably has U % of less than or equal to 1.5%.

The poly(lactic acid) fiber has a high coefficient of friction and istherefore susceptible to fluff during high-speed spinning process, yarntexturing process such as false-twist processing and yarn texturing withair, and fabric making processing such as beaming, weaving, andknitting. To prevent these problems, finishing oil is used finishing oilmainly comprising polyether are not preferably used herein, and thosemainly comprising lubricants such as fatty acid esters are preferred todecrease coefficient of friction of the poly(lactic acid) fiber and toprevent fluff during the above process steps significantly.

The aforementioned process for producing a poly(lactic acid) fiber has avery high production efficiency. This advantage will be described indetail below.

Japanese Unexamined Patent Application Publications No. 8-246247 and No.2000-89938 mention that through-put per unit time during spinning can beused as one of indexes of production efficiency. Specifically, thelarger the product of the spinning speed to yield a fiber with a desireddegree of fineness is, the larger the through-put per unit time andproduction efficiency per unit time are. According to the process forproducing a poly(lactic acid) fiber of the present invention, theundrawn yarn can be obtained at a higher spinning speed and can be drawnat a higher draw ratio than conventional processes and thereby has avery high production efficiency. For example, when an undrawn yarn spunat a spinning speed of 6000 m/min is used, the product of the spinningspeed and the draw ratio is 10500 (Example 4), much higher than theproduct of the spinning speed and the draw ratio of 3600 in theconventional process (Comparative Example 3).

In addition, the process of the present invention can yield, even bysingle-stage drawing and heat treatment, a poly(lactic acid) fiberhaving a strength at 25° C. equivalent to conventional poly(lactic acid)fibers for industrial use produced by conventional multistage drawingand heat treatment. The process can thereby save the cost of equipmentand energy consumption. The process can also be performed according tomultistage drawing and heat treatment procedures according necessity,for example, for the production of an ultrahigh strength poly(lacticacid) fiber.

Some fibers each-comprising a blend of an aromatic polyester and thepoly(lactic acid) have markedly improved mechanical properties at hightemperatures. This type of fibers will be described in detail below.

Aromatic polyesters for use in the present invention are polyesters eachhaving an aromatic ring in its principle chain or side chain andinclude, for example, poly(ethylene terephthalate) (PET), poly(propyleneterephthalate) (PPT), poly(butylene terephthalate) (PBT), andpoly(hexamethylene terephthalate) (PHT).

However, homopoly(ethylene terephthalate) and homopoly(butyleneterephthalate) have low compatibility (miscibility) with aliphaticpolyesters and cannot substantially form polymer blends with suchaliphatic polyesters including poly(lactic acid). To increasecompatibility between an aromatic polyester and the poly(lactic acid),it is effective to introduce an aliphatic comonomer into the principlechain or side chain of the aromatic polyester to thereby increaseaffinity for poly(lactic acid). Alternatively, a bulky moiety isintroduced into the principle chain or side chain of the aromaticpolyester to decrease intercalation between the constitutive aromaticrings to thereby increase intervals or distances between the molecularchains. Preferred examples of the aliphatic comonomer are long alkylchains such as alkylene diols and long-chain dicarboxylic acids, andpreferred examples of the bulky moiety are bisphenol A derivatives. Thealkylene diols include, but are not limited to, polyethylene glycol andother polymers and oligomers of alkylene oxides; and neopentyl glycol,hexamethylene glycol, and other diols each containing a large number ofcarbon atoms. The long-chain dicarboxylic acids include, but are notlimited to, adipic acid and sebacic acid. The amount of the diol or thedicarboxylic acid component in copolymerization is preferably 2% to 15%by mole or 2% to 15% by weight relative to the total amount ofcarboxylic acids or to the total amount of diols, respectively. Theresulting aromatic polyester comprising a copolymerized long alkyl chainor bulky component is hereinafter referred to as “specific aromaticpolyester” for simplicity sake.

In addition, the specific aromatic polyester preferably furthercomprises isophthalic acid or another ingredient as a comonomer to lowerits melting temperature, since the poly(lactic acid) has a melting pointof around 170° C. and blending should preferably be performed at a lowertemperature. The melting point of the specific aromatic polyester ispreferably lower than or equal to 250° C., and more preferably lowerthan or equal to 230° C. In contrast, the melting point is preferablyequal to or higher than 170° C., and more preferably equal to or higherthan 200° C. in order to improve heat resistance of the resulting blendpolyester comprising the poly(lactic acid) and the specific aromaticpolyester (hereinafter briefly referred to as “blend polyester”) and themolded article therefrom.

To improve stability of yarn producing and dimensional stability of theblend polyester, the blend polyester and the constitutive specificaromatic polyester are preferably crystalline. In this connection, whena melting peak of a polymer is observed in differential scanningcalorimetry (DSC), the polymer can be determined as crystalline.

To yield sufficient biodegradability of the blend polyester, the amountof the specific aromatic polyester should preferably be less than orequal to 40% by weight relative to the total weight of the blendpolyester. In contrast, to improve the mechanical properties at hightemperatures, the amount of the specific aromatic polyester ispreferably equal to or more than 5% by weight, and more preferably from15% to 30% by weight.

The mechanical properties at high temperatures of the blend polyesteraccording to the present invention can be improved. This is probably forthe following reasons. A regular poly(lactic acid) has weak interactionbetween molecular chains, the constitutive molecular chains thereby passthrough each other and thereby the poly(lactic acid) exhibitsinsufficient mechanical properties at high temperatures. In contrast, inthe blend polyester, strong interaction between aromatic rings in thespecific aromatic polyester serves to bind and support the poly(lacticacid) molecular chains firmly to thereby improve the mechanicalproperties at high temperatures of the resulting blend polyester fiber.

To further exhibit these advantages, high crystallinity or high T_(g)(glass transition temperature) of the specific aromatic polyester ispreferably utilized in the blend polyester, and the specific aromaticpolyester and the poly(lactic acid) are preferably dissolved in eachother to an appropriate extent.

A first embodiment of such a blend polyester in which the specificaromatic polyester and the poly(lactic acid) are dissolved in each otherto an appropriate extent is a blend polyester of an island-in-seastructure. In this type of the blend polyester, the specific aromaticpolyester and the poly(lactic acid) are phase-separated and constitutean island-in-sea structure in which fine islands each having a diameterof 0.001 to 1 μm are dispersed.

A second embodiment is a blend polyester of a bicontinuous structure asa result of spinodal decomposition. The spinodal decomposition is aprocess in which different types of polymers are once completelydissolved with each other and are then phase-separated. The resultingblend is of the co-continuous structure in which sea and islands cannotsignificantly be distinguished. The bicontinuous structure has anintensity peak (intensity maximum) in Fourier transformation patternanalysis, i.e., has a periodical structure. The second embodiment hereinhaving the co-continuous structure has higher compatibility than that ofthe first embodiment having the island-in-sea structure.

The blend polyester fibers of the present invention have a specialstructure under some conditions.

Specifically, in a blend polyester fiber having such a specialstructure, the poly(lactic acid) enters domains of the specific aromaticpolyester to some extent. In the resulting blend polyester fiber, thespecific aromatic polyester firmly bind the poly(lactic acid). Such aspecial blend structure can be identified, for example, in the followingmanner. The blend polyester fiber is observed with a transmissionelectron microscope (TEM), and the ratio of dark portions (PET) tobright portions (PLA) is determined based on the observed image and iscompared with the charging amount of the poly(lactic acid) to thespecific aromatic polyester. Alternatively, this structure can beidentified based on determination of a long period in small angle X-rayscattering analysis.

For example, TEM observation (FIG. 8) of a blend polyester fibercomprising 80% by weight of poly(lactic acid) and 20% by weight of acopoly(ethylene terephthalate) shown in Example 10 shows that the ratioof bright portions to dark portions is 45:55 (% by area). In contrast, apredicted ratio of the bright portions to the dark portions based on thecharging ratio is 81:19 (% by area). By comparing these two ratios, itis understood that the ratio of the dark portions in the actual blendpolyester fiber is higher than the predicted value, indicating that thepoly(lactic acid) enters into the domains of the copoly(ethyleneterephthalate). In addition, the copoly(ethylene terephthalate) has along period of about 10 nm under normal conditions, but the blendpolyester fiber in Example 10 has an approximately doubled long periodof 19 nm. The result indicates that the molecular chains of thecopoly(ethylene terephthalate) partially sandwich the molecular chainsof the poly(lactic acid).

If the specific aromatic polyester and the poly(lactic acid) arecompletely dissolved with each other at a molecular level, the resultingblend polyester has good spinability but may not exhibit sufficientcrystallinity of the two components or may have insufficiently increasedT_(g) due to additive property of T_(g) in some cases. In these cases,the specific aromatic polyester does not effectively bind thepoly(lactic acid) moiety, and the resulting blend polyester fiber maynot have sufficiently improved mechanical properties at hightemperatures.

In contrast, if the specific aromatic polyester and the poly(lacticacid) have excessively low compatibility with each other, thepoly(lactic acid) cannot enter the domain of the aromatic polyester tothereby fail to exhibit the above advantages and improved mechanicalproperties at high temperatures. In addition, such an immiscible systemfrequently behaves elastically due to phase separation and the resultingblend polyester has markedly deteriorated spinability. The poly(lacticacid) and a homopoly(ethylene terephthalate) or a homopoly(butyleneterephthalate) constitute the immiscible system and cannot substantiallyform a polymer blend.

The poly(lactic-acid) fiber of the present invention may be whichever ofa flat yarn or a crimped yarn. Such a crimped yarn can be produced, forexample, by the following first and second processes.

In the first process, the poly(lactic acid) fiber having excellentmechanical properties at high temperatures is converted into a yarn andis then crimped.

In the second process, the poly(lactic acid) fiber having a crystallinesize in the (200) plane of equal to or more than 6 nm and obtained byspinning at a high speed or the blend polyester fiber comprising thearomatic polyester and the poly(lactic acid) is directly subjected tocrimping. Such crimping operations include, for example, drawfalse-twist texturing, mechanical crimping, and indenting using anair-jet nozzle. In draw false-twist texturing, a heater temperature ispreferably set at equal to or higher than 130° C. to yield a crimpedyarn having high crimping properties and a low shrinkage. By using asecond heater according to necessity, the crimped yarn can becomefurther resistant to shrinkage.

The poly(lactic acid) crimped yarn having satisfactory mechanicalproperties at high temperatures has a crimp rigidity CR of preferablyequal to or more than 10%, more preferably equal to or more than 15%,and further preferably equal to or more than 20%. The crimp rigidity CRis an index of crimp properties.

The poly(lactic acid) fiber of the present invention can have a crosssection of any form such as round, hollow, trefoil, polyfoil, and othermodified cross sections. The fiber is not specifically limited in itsshape and may be, for example, a staple fiber or a filament such as amultifilament and a monofilament. Specifically, the fiber is preferablya multifilament for wide-range applicability.

The poly(lactic acid) fiber of the present invention can be formed intovarious fibrous articles such as woven fabrics, knitted fabrics, andnon-woven fabrics, as well as cups and other molded articles.

The poly(lactic acid) fiber can be advantageously used as material yarnsfor crimping such as false-twist processing and in apparels such asshirts, jumpers and pants, as well as apparel materials such as cups andpads; interiors such as curtains, carpets, mats and furniture; interiorautomotive trims; materials for industrial use such as belts, nets,ropes, canvas, bags and sacks, and threads; felts; nonwoven fabrics;filters; artificial lawn; and other applications.

The poly(lactic acid) fibers having novel structures of the presentinvention have significantly improved mechanical properties at hightemperatures, can thereby solve problems in durability during weavingprocess step or during use in a high-temperature atmosphere and canextend the boundaries in applications of poly(lactic acid) fibers.

EXAMPLES

The present invention will be illustrated in further detail withreference to several examples and comparative examples below, which arenot intended to limit the scope of the invention. The physicalproperties in the following examples and comparative examples weremeasured according to the following methods.

A. Weight Average Molecular Weight of Poly(Lactic Acid)

A solution of a sample in chloroform was mixed with tetrahydrofuran(THF) and thereby yielded a test solution. The weight average molecularweight in terms of polystyrene of the sample in the test solution wasdetermined at 25° C. with a gel permeation chromatograph (GPC) Waters2690 available from Waters Corporation, MA.

B. Tensile Strength and Elongation At Break at 25° C.

According to JIS L 1013 (Test Methods for Man-Made Filament Yarns), aload-elongation curve was obtained at 25° C. at an initial sample lengthof 200 mm at a tensile speed of 200 mm/min. Then, the load was dividedby the initial degree of fineness of the fiber, to be expressed as thestrength, and the elongation was divided by the initial sample length,to be expressed as the elongation. The strength was plotted versus theelongation to yield a strength-elongation curve.

C. Strength at 90° C.

A strength-elongation curve was obtained in the same manner as in “B.Tensile strength and elongation at break at 25° C.”, except that themeasurement was performed at 90° C. The strength at 90° C. wasdetermined by dividing the load at break by the initial degree offineness and was then plotted versus elongation to yield astrength-elongation curve.

D. Creep Rate at 90° C.

The creep rate at 90° C. was determined by reading the elongation at astress of 0.7 cN/dtex in the strength-elongation curve at 90° C.obtained above.

E. Boiling Water Shrinkage

From the yarn package, a hank was taken using a counter wheel, and thehank length L0 measured with a length measurement load of 0.09 cN/dtexapplied. Then this length measurement load was removed and the hankintroduced into boiling water for 15 minutes substantially under noload, after which it was removed, air dried, the length measurement loadagain applied and hank length L1 was measured. The boiling watershrinkage was determined according to the following equation:Boiling water shrinkage (%)=[(L0−L1)/L0]×100

F. Uster Unevenness (U %)

The Uster unevenness (U %) was determined using an USTER TESTER 4available from Zellweger Uster at a yarn supply of 200 m/min, and themean deviation (U %) was determined in normal mode.

G. Solid-State ¹³C-NMR

A ¹³C CP/MAS NMR spectrum was determined under the following conditionsusing a CMX-300 Infinity NMR spectrometer available from Chemagnetics,Varian, Inc. to thereby analyze the carbonyl carbon moiety of esterbond. Observed peaks were subjected to peak resolution by curve fittinginto a peak in the vicinity of 170.2 ppm belonging to the 10₃ helicalstructure and a peak in the vicinity of 171.6 ppm belonging to the 3₁helical structure. The ratio (3₁ ratio) of the integrated intensity ofthe peak in the vicinity of 171.6 ppm to the total integrated intensityof peaks observed at 165 ppm to 175 ppm was determined.

Instrument: CMX-300 Infinity NMR spectrometer available fromChemagnetics, Varian, Inc.

Measuring temperature: room temperature

Reference substance: silicone rubber (internal reference: 1.56 ppm)

Measured nucleus: 75.191:0 MHz

Pulse width: 4.0 μsec

Pulse repetition time: ACQTM (acquisition time)=0.06826 sec, PD (pulsedelay)=5 sec

Data point: POINT=8192, SAMPO=2048

Spectrum width: 30.003 kHz

Pulse mode: relaxation time determination mode

Contact time: 5000 μsec

H. Wide Angle X-ray Diffraction Pattern

A wide angle X-ray diffraction plate image was obtained using an X-raydiffractometer Model 4036 A2 available from Rigaku Corporation under thefollowing conditions:

-   -   X-ray source: Cu-Kα line (with a Ni filter)    -   Output: 40 kV×20 mA    -   Slit: pinhole collimator 1 mm in diameter    -   Camera radius: 40 mm    -   Exposure time: 8 min    -   Film: Kodak DEF-5

I. Crystalline Size

The diffraction intensity in the equatorial direction of a sample wasdetermined using an X-ray diffractometer Model 4036 A2 available fromRigaku Corporation under the following conditions:

-   -   X-ray source: Cu-Kα line (with a Ni filter)    -   Output: 40 kV×20 mA    -   Slit: 2 mmΦ-1°-1°    -   Detector: scintillation counter    -   Counter-recorder: Model RAD-C available from Rigaku Corporation    -   Step scanning: 0.05° step    -   Integration time: 2 seconds

The crystalline size in the (200) plane L was calculated according tothe Scherrer's Formula:L=Kλ/(β₀ cos θ_(B))wherein L is the crystalline size (nm); K is a constant of 1.0; λ is thewavelength of X-ray of 0.15418 nm; θ_(B) is the Bragg angle; and β₀ isrepresented by (β_(E) ²−B₁ ²)^(1/2), wherein β_(E) is the apparenthalf-width (measured value); and β₁ is the constant specific to theinstrument of 1.046×10⁻² rad.

J. Crystalline Orientation

The crystalline orientation in the (200) plane was determined in thefollowing manner.

A peak corresponding to the (200) plane was scanned in thecircumferential direction to yield an intensity distribution, and thecrystalline orientation was calculated from the half width obtained inthe intensity distribution according to the following equation:Crystalline orientation (π)=(180-H)/180wherein H is the half width (deg.).

-   -   Measuring range: 0° to 180°    -   Step-scanning: 0.5° step    -   Integration time: 2 seconds

K. Crimp Rigidity CR of False-Twisted Yarn

A false-twisted yarn was wound on a spool to make a skein, was allowedto freely shrink in boiling water under substantially no load for 15minutes and was air-dried for 24 hours. The resulting sample wasimmersed in water-under a load equivalent to 0.088 cN/dtex (0.1 gf/d),and the skein length L′0 was determined 2 minutes later. The skeinequivalent to 0.088 cN/dtex was removed in water, the load was thenreplaced with a light load equivalent to 0.0018 cN/dtex (2 mgf/d), andthe skein length L′1 was determined 2 minutes later. Based on thesemeasurements, the crimp rigidity CR was calculated according to thefollowing equation:CR (%)=[(L′0−L′1)/L′0]×100

Examples 1 and 2

A poly(L-lactic acid) having a weight average molecular weight of 190000and an optical purity as L-lactic acid of 9.9% was dried, was subjectedto melt spinning at 240° C., the resulting yarn was cooled andsolidified with a cooling air at 25° C. using a chimney 4. Finishing oilmainly containing aliphatic esters was applied to the solidified yarnusing a bundling-oiling guide 6, and the yarn was then entangled with aninterlacing guide 7 (FIG. 9). The resulting undrawn yarn 10 was thenreeled with an unheated first take-up roller 8 at a peripheral speed of5000 m/min., i.e., a spinning speed of 5000 m/min. and was then reeledvia an unheated second take-up roller 9. The reeled homopoly(L-lacticacid) undrawn yarn had a crystalline size in the (200) plane of 7.7 nm,a crystalline orientation of 0.96, U % of 0.8%, and an elongation at 25°C. of 50%. The undrawn yarn 10 was drawn and heat-treated using theapparatus shown in FIG. 10 under the conditions indicated in Table 1 andthereby yielded 84 dtex-24 filament drawn yarns each having a roundcross section.

FIG. 5 illustrates solid-state NMR spectra of these drawn yarns. A clearpeak in the vicinity of 171.6 ppm belonging to the 3₁ helical structurewas observed in the fiber according to Example 1, and a shoulder peakcorresponding thereto was observed in the fiber according to Example 2.These spectra were subjected to peak resolution, and the ratios of theintegrated intensity of the peak in the vicinity of 171.6 ppm (3₁ratios) were determined to find that the 3₁ ratios were 29% and 17% inExamples 1 and 2, respectively (FIG. 6). The fibers were subjected towide angle X-ray diffractometry (WAXD). The fiber of Example 1 was foundto show a pattern analogous to the beta crystal described inMacromolecules, vol. 23, 642 (1990), showing that a crystalline havingthe 3₁ helical structure was produced (FIG. 7). In contrast, the fiberof Example 2 did not show a pattern of a crystalline having the 3₁helical structure. The strength-elongation curve at 90° C. and thephysical properties of the fiber of Example 1 are shown in FIG. 1 andTable 1, respectively. These results demonstrate that the fiber ofExample 1 have markedly improved mechanical properties at 90° C. ascompared with a conventional high-strength poly(lactic acid) fiber(Comparative Example 1). The strength-elongation curve at 90° C. and thephysical properties of the fiber of Example 2 are shown in FIG. 2 andTable 1, respectively. These results demonstrate that the fiber ofExample 2 have markedly improved mechanical properties at 90° C. ascompared with a conventional poly(lactic acid) fiber (ComparativeExample 3). The fiber of Example 2 had an elongation of 8% at 90° C. ata stress of 0.5 cN/dtex.

Examples 3 and 4

The spinning and drawing procedures of Example 1 were repeated exceptthat the spinning speed was changed to 6000 m/min and thereby yielded 84dtex-96 filament drawn yarns. An undrawn yarn prepared herein had acrystalline size in the (200) plane of 9.2 nm, a crystalline orientationof 0.96, U % of 0.8%, and an elongation at 25° C. of 43%.

The solid-state NMR spectra of the drawn yarns demonstrate that theyhave the 31 helical structure. Table 1 shows the physical properties ofthese drawn yarns and demonstrates that they have significantly improvedmechanical properties at 90° C. as compared with the conventionalhigh-strength poly(lactic acid) fiber (Comparative Example 1).

Example 5

The spinning and drawing procedures of Example 1 were repeated exceptthat the peripheral speed of the first take-up roller 8, the temperatureof the first hot roller 12 in drawing process, and the draw ratio werechanged to 4000 m/min, 110° C., and 1.6, respectively, and therebyyielded a 84 dtex-36 filament homopoly(L-lactic acid) drawn yarn havingtrefoil cross section. A reeled yarn after spinning herein had acrystalline size in the (200) plane of 6.8 nm, a crystalline orientationof 0.91, U % of 0.8%, and an elongation at 25° C. of 72%. Thesolid-state NMR spectrum of resulting drawn yarn demonstrates that ithas the 3₁ helical structure. Table 1 shows the physical properties ofthe drawn yarn and demonstrates that it has improved mechanicalproperties at 90° C. as compared with the conventional high-strengthpoly(lactic acid) fiber (Comparative Example 1). The fiber of Example 5had an elongation of 12% at 90° C. at a stress of 0.5 cN/dtex.

Example 6

The spinning and drawing procedures of Example 1 were repeated exceptthat the peripheral speed of the first take-up roller 8, the temperatureof the first hot roller 12 in drawing process, and the draw ratio werechanged to 3000 m/min, 140° C., and 2.05, respectively, and therebyyielded a 84 dtex-24 filament homopoly(L-lactic acid) drawn yarn havinga round cross section. An undrawn yarn prepared herein did not exhibit acrystalline pattern in WAXD, indicating that it was non-crystalline. Theundrawn yarn had U % of 1.1% and an elongation at 25° C. of 95%. Theyarn therefore showed some degree of instability of yarn running on thefirst hot roller but it was trivial.

The solid-state NMR spectrum of resulting drawn yarn demonstrates thatit has the 3₁ helical structure. Table 1 shows the physical propertiesof the drawn yarn and demonstrates that it has improved mechanicalproperties at 90° C. as compared with the conventional high-strengthpoly(lactic acid) fiber (Comparative Example 1).

Comparative Example 1

A poly(L-lactic acid) having a weight average molecular weight of 150000and an optical purity as L-lactic acid of 99% was subjected tothree-stage drawing and heat treatment according to the processdescribed in Example 9 of Japanese Unexamined Patent ApplicationPublication No. 2000-248426 and thereby yielded a high strengthpoly(lactic acid) fiber. The conditions in this procedure are asfollows: spinning speed of undrawn yarn of 2200 m/min, drawingtemperature at first stage of 82° C., drawing temperature at secondstage of 130° C., drawing temperature at third stage of 160° C., drawratio at the first stage of 1.53, draw ratio at the second stage of1.55, draw ratio at the third stage of 1.55, and final heatingtemperature of 155° C.

The solid-state NMR spectrum of the resulting drawn yarn did not exhibita peak in the vicinity of 171.6 ppm corresponding to the 3₁ helicalstructure (FIG. 5). The drawn yarn was then subjected to wide angleX-ray diffractometry but only yielded a pattern corresponding to theregular alpha crystal (10₃ helical structure), although it was found tobe highly crystallized. Table 1 shows the physical property of the drawnyarn and demonstrates that it has insufficient mechanical properties at90° C. although it has high strength at room temperature.

Comparative Examples 2 and 3

Poly(lactic acid) undrawn yarns were obtained in the same manner as inExample 1, except employing the spinning speeds indicated in Table 1.The undrawn yarns were non-crystalline and their crystalline sizes couldnot be determined. The undrawn yarns obtained at a spinning speed of 400m/min (Comparative Example 2) and at a spinning speed of 1500 m/min(Comparative Example 3) had U % of 1.7% and 1.3%, respectively. Theseundrawn yarns were subjected to drawing and heat treatment in the samemanner as in Example 1 under the conditions shown in Table 1 and therebyyielded 84 dtex-24 filament drawn yarns each having a round crosssection.

The solid-state NMR spectra of the resulting drawn yarns did not exhibita peak: in the vicinity of 171.6 ppm corresponding to the 3₁ helicalstructure. The drawn yarns were then subjected to wide angle X-raydiffractometry but only yielded a pattern corresponding to the regularalpha crystal (10₃ helical structure), although they were found to behighly crystallized. Table 1 shows the physical property of the drawnyarns and demonstrates that they have insufficient mechanical propertiesat 90° C. although they have high strength at room temperature.

Comparative Example 4

The properties of the undrawn yarn obtained in Example 1 at a spinningspeed of 5000 m/min without drawing and heat treatment were determined.The solid-state NMR spectrum of the undrawn yarn did not exhibit a peakin the vicinity of 171.6 ppm corresponding to the 3₁ helical structure.The undrawn yarn was then subjected to wide angle X-ray diffractometrybut only yielded a pattern corresponding to the regular alpha crystal(10₃ helical structure), although it was found to be highlycrystallized. Table 1 shows the physical property of the undrawn yarnand demonstrates that it has insufficient mechanical properties at 90°C.

-   TABLE 1

Comparative Example 5

A poly(L-lactic acid) having a weight average molecular weight of 140000and an optical purity as L-lactic acid of 99% was dried, was thensubjected to melt spinning at 210° C. using the apparatus shown in FIG.12, the resulting yarn was cooled and solidified with a cooling air at15° C. using the chimney 4. The yarn was then passed through a tubularheater 24 at an inner wall temperature of 150° C. having an effectiveheating length of 130 cm and was left stand to cooling. Finishing oilwas then applied to the yarn using the bundling-oiling guide 6, and theyarn was entangled by the interlacing guide 7. The resulting yarn 10 wasthen taken up with the unheated first take-up roller 25 at a peripheralspeed of 4500 m/min and was then reeled at a speed of 4470 m/min via thesecond take-up roller 26 at 110° C. at a peripheral speed of 4550 m/minand thereby yielded a 84 dtex-36 filament yarn 27 having a round crosssection. The resulting yarn has low strength at 90° C. of 0.5 cN/dtexalthough it has a high strength at 25° C. of 4.5 cN/dtex.

Comparative Example 6

A 84 dtex-36 filament yarn 27 having a round cross section was obtainedby the spinning procedure of Comparative Example 5, except that thetubular heater 24 was not used, that the yarn was reeled at a speed of4490 m/min. via the first take-up roller 25 at a peripheral speed of3500 m/min and via the second take-up roller 26 at a peripheral speed of4550 m/min. Table 1 shows the physical properties of the resulting yarnand demonstrates that it has a significantly low strength at 90° C. of0.3 cN/dtex.

Comparative Example 7

A poly(L-lactic acid) having a weight average molecular weight of 140000and an optical purity as L-lactic acid of 99% was dried and was kneadedwith 2.5% by weight of silica having an average grain size of 0.045 μmin a twin-screw extruder. The resulting polymer was dried and wassubjected to melt spinning using an apparatus shown in FIG. 13.Specifically, the polymer was melted at 250° C. and was spun at asingle-orifice through-put of 1.39 g/min. from a die orifice 0.25 mm indiameter, the resulting yarn was cooled and solidified with a coolingair at 15° C. using the chimney 4. The yarn was then passed through thetubular heater 24 at an inner wall temperature of 200° C. and was leftstand to cool. The tubular heater 24 was arranged 1.2 m beneath the dieand had a length of 1.0 m, an inlet diameter of 8 mm, and an innerdiameter of 30 mm. Finishing oil was then applied to the yarn using thebundling-oiling guide 6, and the yarn was entangled by the interlacingguide 7. The resulting yarn was taken up with an unheated first take-uproller 8 at a peripheral speed of 4000 m/min., was reeled via a secondtake-up roller 9 and thereby yielded a 84 dtex-24 filament yarn 10having a round cross section. The resulting yarn has low strength at 90°C. of 0.5 cN/dtex.

Example 7

The spinning and drawing procedures of Example 1 were repeated, exceptthat a poly(L-lactic acid) having a weight average molecular weight of140000 and an optical purity as L-lactic acid of 99% was subjected tomelt spinning at 220° C., and thereby yielded a 84 dtex-24 filamentdrawn yarn having a hollow round cross section (hollowness percentage:15%). An undrawn yarn prepared herein had a crystalline size in the(200) plane of 7.7 nm, a crystalline orientation of 0.96, U % of 1.2%,and an elongation at 25° C. of 47%. The solid-state spectrum of thedrawn yarn demonstrates that it has the 3₁ helical structure. Table 2shows the physical properties of the drawn yarn and demonstrates that ithas significantly improved mechanical properties at 90° C. as comparedwith the conventional high-strength poly(lactic acid) fiber (ComparativeExample 1). The fiber of Example 7 has an elongation of 10% at 90° C.under a stress of 0.5 cN/dtex.

Example 8

A poly(L-lactic acid) having a weight average molecular weight of 140000and an optical purity as L-lactic acid of 99% was dried and wassubjected to melt spinning at 220° C. in the same manner as in Example 1and thereby yielded an undrawn yarn. The undrawn yarn had a crystallinesize in the (200) plane of 7.7 nm, a crystalline orientation of 0.94, U% of 1.0%, and an elongation at 25° C. of 49%. The undrawn yarn was thensubjected to drawing and heat treatment in a similar manner to that inExample 1 under the condition indicated in Table 2 and thereby yielded a84 dtex-36 filament drawn yarn having a trefoil cross section.

The solid-state NMR spectrum of the drawn yarn shows that it has the 3₁helical structure. Table 2 shows the physical properties of the drawnyarn and demonstrates that it has significantly improved mechanicalproperties at 90° C. as compared with the conventional high-strengthpoly(lactic acid) fiber (Comparative Example 1).

Example 9

The melt spinning, drawing and heat treatment procedures of Example 8were repeated under the condition indicated in Table 2 and therebyyielded a 84 dtex-36 filament drawn yarn having a hollow cross section(hollowness percentage: 20%). An undrawn yarn prepared herein had acrystalline size in the (200) plane of 7.6 nm, a crystalline orientationof 0.94, U % of 1.2%, and an elongation at 25° C. of 46%.

The solid-state NMR spectrum of the drawn yarn shows that it has the 3₁helical structure. Table 2 shows the physical properties of the drawnyarn and demonstrates that it has significantly improved mechanicalproperties at 90° C. as compared with the conventional high-strengthpoly(lactic acid) fiber (Comparative Example 1).

-   TABLE 2

Example 10

A copoly(ethylene terephthalate) having an intrinsic viscosity of 0.65and a melting point of 220° C. was prepared by copolymerization with 6%by mole of a bisphenol A-ethylene oxide adduct as an alkylene oxide and6% by mole of isophthalic acid. The poly(lactic acid) used in Example 7was dried and was melted and blended with the copoly(ethyleneterephthalate) at 235° C. in a twin-screw extruder and thereby yieldedblend polymer chips. The amount of the copoly(ethylene terephthalate)was 20% by weight based on the weight of the resulting blend polymer.The blend polymer chips had T_(g) of 61° C., nearly equivalent to thatof a homopoly(L-lactic acid), i.e., 60° C. The blend polymer chips weredried, were subjected to melt spinning at a pinning temperature of 235°C., the resulting yarn was cooled and solidified with a cooling air at25° C. using the chimney 4. Finishing oil was then applied to the yarnusing the bundling-oiling guide 6, and the yarn was entangled by theinterlacing guide 7 (FIG. 9). The resulting yarn was taken up with theunheated first take-up roller 8 at a peripheral speed of 1500 m/min andwas then reeled via the unheated second take-up roller 9. The reeledyarn was pre-heated with a first hot roller 12 at a temperature of 90°C., was drawn at a draw ratio of 2.8, was heat-set with a second hotroller 13 at 130° C., was reeled by an unheated third roller 14 andthereby yielded a 84 dtex-36 filament drawn yarn 15 having a round crosssection (FIG. 10). The strength-elongation curve at 90° C. and thephysical properties of the drawn yarn are shown in FIG. 2 and Table 3,respectively. These results demonstrate that the drawn yarn of Example10 has a higher yield stress and significantly improved mechanicalproperties at 90° C. as compared with the conventional poly(lactic acid)fiber (Comparative Example 3). The wide angle X-ray diffractometry ofthe drawn yarn shows that the copoly(ethylene terephthalate) constitutesan oriented crystalline. The drawn yarn had an elongation of 7% at 90°C. under a stress of 0.5 cN/dtex.

Example 11

A copoly(ethylene terephthalate) having an intrinsic viscosity of 0.55and a melting point of 240° C. was prepared by copolymerization with 4%by mole of polyethylene glycol having a molecular weight of 1000 and 6%by mole of isophthalic acid. The prepared copoly(ethylene terephthalate)and the dried poly(lactic acid) used in Example 1 were melted andblended at 250° C. in a twin-screw extruder and thereby yielded blendpolymer chips. The amount of the copoly(ethylene terephthalate) was 20%by weight based on the weight of the resulting blend polymer. The blendpolymer chips were dried and were spun and drawn in the same manner asin Example 10, except that the spinning temperature was changed to 250°C., and thereby yielded a 164 dtex-48 filament drawn yarn having a roundcross section. Table 3 shows the physical properties of the drawn yarnand demonstrates that it has markedly improved mechanical properties at90° C. as compared with the conventional poly(lactic acid) fiber(Comparative Example 3). The drawn yarn had an elongation of 5% at 90°C. under a stress of 0.5 cN/dtex.

Example 12

A copoly(ethylene terephthalate) having an intrinsic viscosity of 0.65and a melting point of 225° C. was prepared by copolymerization with 10%by mole of adipic acid and 6% by mole of isophthalic acid. The preparedcopoly(ethylene terephthalate) and the dried poly(lactic acid) used inExample 1 were melted and blended at 235° C. in a twin-screw extruderand thereby yielded blend polymer chips. The amount of thecopoly(ethylene terephthalate) was 20% by weight based on the weight ofthe resulting blend polymer. The blend polymer chips were dried and werespun and drawn in the same manner as in Example 10 and thereby yielded a84 dtex-48 filament drawn yarn having a round cross section. Table 3shows the physical properties of the drawn yarn and demonstrates that ithas markedly improved mechanical properties at 90° C. as compared withthe conventional poly(lactic acid) fiber (Comparative Example 3). Thedrawn yarn had an elongation of 6% at 90° C. under a stress of 0.5cN/dtex.

Comparative Example 8

A nylon 6 having a relative viscosity of 3.4 and the dried poly(lacticacid) used in Example 1 were melted and blended at 245° C. in atwin-screw extruder and thereby yielded blend polymer chips. The amountof nylon 6 was 10% by weight based on the total weight of the resultingblend polymer. The blend polymer chips were dried and were melted andspun in the same manner as in Example 10, except that the spinningtemperature was changed to 245° C. During this procedure., the yarnfrequently broke, since nylon 6 and the poly(lactic acid) haveinsufficient compatibility with each other. The reeled undrawn yarn 10was pre-heated with the first hot roller 12 at a temperature of 90° C.,was drawn at a draw ratio of 1.5, was heat-set with the second hotroller 13 at 130° C., was reeled by the unheated third roller 14 andthereby yielded a 100 dtex-36 filament drawn yarn 15 having a roundcross section. The yarn was not satisfactorily drawn and frequentlybroke during drawing procedure. Table 3 shows the physical properties ofthe yarn and demonstrates that it has low strength at room temperatureand poor mechanical properties at 90° C.

Comparative Example 9

In this example, poly(methyl methacrylate) (PMMA) as a polymer that canbe completely dissolved with poly(lactic acid) and has a high T_(g) wasblended with the poly(lactic acid). Specifically, a PMMA (available fromSumitomo Chemical Co., Ltd., under the trade name of SUMIPEK LG21) andthe dried poly(lactic acid) used in Example 7 were melted and blended at220° C. in a twin-screw extruder and thereby yielded blend polymerchips. The amount of PMMA was 50% by weight based on the total weight ofthe resulting blend polymer. The blend polymer chips had T_(g) of 75°C., much higher than that of homopoly(L-lactic acid), i.e., 60° C. Theblend polymer chips were dried, were subjected to melt spinning at aspinning temperature of 220° C. in the same manner as in Example 10. Thereeled undrawn yarn 10 was pre-heated with the first hot roller 12 at atemperature of 90° C., was drawn at a draw ratio of 1.7, was heat-setwith the second hot roller 13 at 130° C., was reeled via the unheatedthird roller 14 and thereby yielded a 100 dtex-36 filament drawn yarn 15having a round cross section. Table 3 shows the physical properties ofthe yarn and demonstrates that it has low strength at room temperatureand poor mechanical properties at 90° C., indicating that increasedT_(g) of a polymer does not always contribute to improvement inmechanical properties at high temperatures.

Comparative Example 10

A blend polymer chips having T_(g) of 66° C. were prepared by polymerblending procedure of Comparative Example 9, except that the amount ofPMMA was changed to 30% by weight. The blend polymer chips were spun anddrawn in the same manner as in Comparative Example 6, except that thedraw ratio was changed to 2.8, and thereby yielded a 84 dtex-36 filamentdrawn yarn having a round cross section. Table 3 shows the physicalproperties of the drawn yarn and demonstrates that it has insufficientmechanical properties at 90° C., as in Comparative Example 9.

Comparative Example 11

An aliphatic polyester carbonate containing 14% of a carbonate unit andhaving a weight average molecular weight of 190000 was prepared bypolymerization according to the procedure described in Example 2 ofJapanese Unexamined Patent Application Publication No. 2000-109664. Thealiphatic polyester carbonate and a dried homopoly(L-lactic acid) havingan optical purity of 99% and a weight average molecular weight of 200000were melted and blended at 240° C. in a twin-screw extruder and therebyyielded blend polymer chips having T_(g) of 65° C. The amount of thealiphatic polyester carbonate was 50% by weight based on the totalweight of the resulting blend polymer. The blend polymer chips weredried and were melted and spun in the same manner as in Example 10,except that the spinning temperature was changed to 240° C. During thisprocedure, the yarn frequently broke, since the aliphatic polyestercarbonate and the poly(lactic acid) have insufficient compatibility witheach other. The reeled undrawn yarn was pre-heated with the first hotroller 12 at a temperature of 90° C., was drawn at a draw ratio of 1.5,was heat-set with the second hot roller 13 at 130° C., was reeled viathe unheated third roller 14 and thereby yielded a 100 dtex-36 filamentdrawn yarn 15 having a round cross section. The yarn was notsatisfactorily drawn and frequently broke during drawing procedure.Table 3 shows the physical properties of the drawn yarn and demonstratesthat it has low strength at room temperature and poor mechanicalproperties at 90° C.

Comparative Example 12

A dried nylon 11 having an intrinsic viscosity of 1.45 and the driedhomopoly(L-lactic acid) used in Example 7 were melted separately andwere subjected to spinning at 220° C. to yield a core-sheath conjugateyarn comprising nylon 11 as a core component and the homopoly(L-lacticacid) as a sheath component. The amount of nylon 11 herein was 20% byweight based on the total weight of the resulting conjugate yarn. Thespun yarn was then drawn in the same manner as in Example 10 and therebyyielded a 84 dtex-24 filament drawn yarn having a round cross section.Table 3 shows the physical properties of the drawn yarn and demonstratesthat it has low mechanical properties at 90° C.

Comparative Example 13

A 84 dtex-24 filament drawn yarn having a round cross section wasprepared by the spinning and drawing procedures of Comparative Example12, except that a poly(butylene terephthalate) having an intrinsicviscosity of 1.0 was used instead of nylon 11 and the spinningtemperature was changed to 250° C. Table 3 shows the physical propertiesof the drawn yarn and demonstrates that it has low mechanical propertiesat 90° C.

Comparative Example 14

A 84 dtex-24 filament drawn yarn having a round cross section wasprepared by the spinning and drawing procedures of Comparative Example12, except that a poly(ethylene terephthalate) having an intrinsicviscosity of 0.65 was used instead of nylon 11 and the spinningtemperature was changed to 290° C. Table 3 shows the physical propertiesof the drawn yarn and demonstrates that it has insufficient strength atroom temperature and low mechanical properties at 90° C., since thepoly(lactic acid) was significantly decomposed during spinning at a hightemperature.

-   TABLE 3

Example 13

The poly(lactic acid) drawn yarn obtained in Example 2 was subjected todraw false-twist operation using the apparatus shown in FIG. 11 underthe conditions indicated in Table 4. The speed of the drawing roller 20,i.e., the processing speed was set at 400 m/min, and the second heater21 was not used. A triaxial twister was used as a false-twist rotor 19.Table 4 shows the physical properties of the resulting yarn anddemonstrates that it has satisfactory strength at 90° C. and excellentcrimp properties and boiling water shrinkage.

Example 14

The undrawn yarn obtained in Example 2 was subjected to draw false-twistoperation in the same manner as in Example 13 under the conditionsindicated in Table 4. Table 4 shows the physical properties of theresulting draw false-twist yarn and demonstrates that it hassatisfactory strength at 90° C. and excellent crimp properties andboiling water shrinkage. FIG. 14 shows the strength-elongation curve ofthe draw false-twist yarn.

Example 15

A false-twist yarn was prepared in the same manner as in Example 14,except that the temperature of the second heater 14 was set at 150° C.and a relax rate between a drawing roller 20 and a delivery roller 22was set at 6%. Table 4 shows the physical properties of the false-twistyarn and demonstrates that it becomes resistant to shrinkage and has alow boiling water shrinkage of 6% by action of the second hater.

Example 16

The undrawn yarn obtained in Example 8 was subjected to draw false-twistoperation in the same manner as in Example 15 under the conditionsindicated in Table 4, except that a relax rate between the drawingroller 20 and a delivery roller 22 was set at 3%. Table 4 shows thephysical properties of the false-twist yarn and demonstrates that itbecomes resistant to shrinkage and has a low boiling water shrinkage of7% by action of the second hater.

Example 17

The drawn yarn obtained in Example 10 was subjected to draw false-twistin the same manner as in Example 13 under the conditions indicated inTable 4. Table 4 shows the physical properties of the resultingfalse-twist yarn and demonstrates that it has satisfactory strength at90° C. and excellent crimp properties and boiling water shrinkage.

Comparative Example 15

The conventional poly(lactic acid) fiber obtained in Comparative Example3 was subjected to draw false-twist operation in the same manner as inExample 13 at a draw ratio of 1.5 and a heater temperature of 130° C.,but the yarn broke on the heater 17 and could not be held by a threadguard. Next, the temperature of the heater 17 was reduced to 110° C. andthe poly(lactic acid) fiber was again subjected to draw false-twistoperation. In this case, the yarn could be reeled although the yarn wasinsufficiently held by the thread guard. The resulting false-twist yarnhas a crimp rigidity CR of 20% but low.strength at 90° C. FIG. 15illustrates the strength-elongation curve of the false-twist yarn.

Comparative Example 16

The conventional poly(lactic acid) fiber obtained in Comparative Example3 was subjected draw false-twist operation in the same manner as inComparative Example 15, except that the temperature of the second heater21 was set at 150° C. and the relax rate between the drawing roller 20and the delivery roller 22 was set at 8%, and thereby yielded afalse-twist yarn. Table 4 shows the physical properties of thefalse-twist yarn and demonstrates that it becomes resistant to shrinkageand has a low boiling water shrinkage of 8% by action of the secondhater but it becomes nearly free of crimp to have a crimp rigidity CR of3%. In addition, the false-twist yarn has low strength at 90° C.

Comparative Example 17

An undrawn yarn was prepared and reeled in the same manner as in Example8 at a spinning speed of 3000 m/min. The wide angle X-ray diffractometryof the reeled undrawn yarn shows that it does not exhibit a crystallinepattern and is non-crystalline. The undrawn yarn had U % of 1.1% and anelongation at 25° C. of 97%. The undrawn yarn was subjected as amaterial yarn to draw false-twist operation in the same manner as inExample 13, but the yarn broke on the heater 17 and could not be held bya thread guard. Next, the temperature of the heater 17 was reduced to110° C. and the poly(lactic acid) fiber was again subjected to drawfalse-twist operation. In this case, the yarn could be reeled althoughthe yarn was insufficiently held by the thread guard. The resultingfalse-twist yarn has low strength at 90° C.

-   TABLE 4

Example 18

A plain weave fabric was prepared using the yarn obtained in Example 1as the warp and weft. The warp was sized and dried at 110° C. withoutany troubles such as fluff and elongation of yarn. The plain weavefabric was scoured at 60° C. according to a conventional procedure, wassubjected to pre-setting at 140° C., and was dyed at 110° C. accordingto a conventional procedure. The resulting fabric has satisfactory feel(texture) as apparel, such as the feel of rustle and a soft feel.

The yarns obtained according to Examples 2 to 17 were woven and theresulting plain woven fabrics were evaluated as fabrics in the samemanner as above. Fluff, elongation of yarn and other troubles did notoccur and the resulting fabrics satisfactory feel (texture) as apparel,such as the feel of rustle and a soft feel.

Comparative Example 18

A plain weave fabric was prepared in the same manner as in Example 18,except that the yarn obtained according to Comparative Example 3 wasused as the warp and weft. In this procedure, the warp was sized anddried at 110° C., but it elongated and could not be dried.

Example 19

The poly(lactic acid) used in Example 1 was blended homogeneously with1% of ethylenebis(stearamide) as a lubricant in a twin-screw extruder ata kneading temperature of 230° C. and thereby yielded chips. The chipswere melted and spun in the same manner as in Example 3 and therebyyielded an undrawn yarn. The undrawn yarn had a crystalline size in the(200) plane of 9.3 nm, a crystalline orientation of 0.96, U % of 0.8%,and an elongation at 25° C. of 43%. The undrawn yarn was then subjectedto drawing and heat treatment in the same manner as in Example 3 andthereby yielded a drawn yarn. The drawn yarn had a satisfactory strengthat 90° C. of 1.5 cN/dtex.

Example 20

An undrawn yarn was prepared by the melt spinning procedure of Example19, except that the amount of ethylenebis(stearamide) was changed to0.5%. The undrawn yarn had a crystalline size in the (200) plane of 9.2nm, a crystalline orientation of 0.96, U % of 0.8%, and an elongation at25° C. of 43%. The undrawn yarn was then subjected to drawing and heattreatment in the same manner as in Example 19 and thereby yielded adrawn yarn. The drawn yarn had a satisfactory strength at 90° C. of 1.5cN/dtex.

Example 21

An undrawn yarn was prepared by the melt spinning procedure of Example20, except that the amount of ethylenebis(stearamide) was changed to 3%.The undrawn yarn had a crystalline size in the (200) plane of 9.3 nm, acrystalline orientation of 0.96, U % of 0.8%, and an elongation at 25°C. of 43%. The undrawn yarn was then subjected to drawing and heattreatment in the same manner as in Example 19 and thereby yielded adrawn yarn. The drawn yarn had a satisfactory strength at 90° C. of 1.5cN/dtex.

Example 22

The undrawn yarn obtained in Example 19 was subjected to the drawfalse-twist procedure of Example 15, except that the draw ratio waschanged to 1.30. The resulting crimped yarn has satisfactory propertiesincluding a crimp rigidity CR of 22%, a strength at 25° C. of 2.9cN/dtex, an elongation at 25° C. of 23%, a strength at 90° C. of 1.0cN/dtex, a boiling water shrinkage of 4%, and U % of 1.0%.

-   TABLE 5

Example 23

Plain weave fabrics were prepared in the same manner as in Example 18 byusing the poly(lactic acid) fibers obtained in Examples 19 to 22. Theresulting fabrics were rubbed with a cotton cloth 300 times but theyexhibit no becoming a cotton cloth colored and no fluff in them. And ithad satisfactory wear resistance.

Comparative Example 19

Plain weave fabrics were prepared in the same manner as in Example 23 byusing the poly(lactic acid) fibers obtained in Comparative Example 3.The resulting fabrics were rubbed with a cotton cloth 300 times in thesame manner as in Example 23. It exhibits becoming a cotton clothvigorously colored and many fluffs in it. And it had poor wearresistance.

While the present invention has been described with reference to whatare presently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the sprit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions. TABLE 1 SpinningStrength Strength Creep speed 1 HR Draw 2 HR 3₁ Ratio 3₁ at 25° C.Elongation at 90° C. rate at SW (m/min) (° C.) ratio E (° C.) (%)Crystal U % (%) (cN/dtex) at 25° C. (%) (cN/dtex) 90° C. (%) (%) Ex. 15000 140 1.84 0.50 130 29 yes 1.0 6.1 19 2.1 4 9 (1.34+E) Ex. 2 5000 1401.50 0.50 130 17 no 0.9 3.8 30 1.3 11 7 (1.00+E) Ex. 3 6000 90 1.44 0.43130 12 no 1.2 4.2 22 1.3 11 4 (1.01+E) Ex. 4 6000 140 1.75 0.43 150 33yes 1.0 5.7 18 2.1 4 6 (1.32+E) Ex. 5 4000 110 1.60 0.72 130 10 no 1.03.3 40 0.8 15 5 (0.88+E) Ex. 6 3000 140 2.05 0.95 130 18 yes 1.2 4.8 222.2 5 10 (1.10+E) Com. 2200 three-stage (first 1.20 130 0 no 1.8 7.0 270.7 7 8 Ex. 1 drawing stage: 0.33+E) Com. 400 120 4.90 2.50 125 0 no 5.27.5 30 0.4 — 17 Ex. 2 (2.40+E) Com. 1500 90 2.40 1.65 130 0 no 2.9 3.650 0.3 — 11 Ex. 3 (0.75+E) Com. 5000 undrawn 0 no 0.8 2.4 50 0.4 — 18Ex. 4 yarn1 HR: First hot roller temperature,2 HR: Second hot roller temperatureDraw ratio: The ratio of peripheral speed of the second hot roller tothat of the first hot rollerE: [Elongation (%) of undrawn yarn]/1003₁ Ratio (%): The ratio of 3₁ helical structure to the total fiber asdetermined by solid-state NMR3₁ Crystal: The presence of a crystal of the 3₁ helical structure asdetermined by WAXDSW: Boiling water shrinkage

TABLE 2 3₁ Strength Elongation Strength at Creep 1 HR Draw 2 HR Ratio 3₁at 25° C. at 25° C. 90° C. rate at (° C.) ratio E (° C.) (%) Crystal U %(%) (cN/dtex) (%) (cN/dtex) 90° C. (%) SW (%) Ex. 7 140 1.50 0.47 130 16no 0.9 3.4 35 1.0 12 7 (1.03+E) Ex. 8 130 1.75 0.49 150 25 yes 1.0 5.620 1.9 5 5 (1.26+E) Ex. 9 130 1.67 0.46 150 24 yes 1.2 5.2 20 1.7 5 5(1.21+E)1 HR: First hot roller temperature,2 HR: Second hot roller temperatureDraw ratio: The ratio of peripheral speed of the second hot roller tothat of the first hot rollerE: [Elongation (%) of undrawn yarn]/1003₁ Ratio (%): The ratio of 3₁ helical structure to the total fiber asdetermined by solid-state NMR3₁ Crystal: The presence of a crystal of the 3₁ helical structure asdetermined by WAXDSW: Boiling water shrinkage

TABLE 3 Strength at Elongation at Strength at Creep rate 25° C.(cN/dtex) 25° C. (%) 90° C. (cN/dtex) at 90° C. (%) SW (%) U % (%) Ex.10 3.0 45 1.0 8 5 1.0 Ex. 11 2.6 40 1.0 6 7 1.0 Ex. 12 3.1 42 1.0 7 91.0 Com. Ex. 8 1.9 72 0.3 broken 6 4.5 Com. Ex. 9 2.3 70 0.3 broken 132.5 Com. Ex. 10 2.7 63 0.4 broken 11 2.1 Com. Ex. 11 1.8 75 0.3 broken10 3.5 Com. Ex. 12 2.8 60 0.4 broken 7 2.3 Com. Ex. 13 3.1 62 0.4 broken7 1.5 Com. Ex. 14 1.7 45 0.5 broken 5 2.5SW: Boiling water shrinkage

TABLE 4 Strength Strength at 1 H Draw 2 H CR at 25° C. Elongation 90° C.Material yarn (° C.) ratio (° C.) (%) (cN/dtex) at 25° C. (%) (cN/dtex)SW (%) U % (%) Ex. 13 drawn yarn of 130 1.10 — 25 3.5 19 0.9 5 0.9 Ex. 2Ex. 14 undrawn yarn of 130 1.30 — 24 3.0 22 0.8 15 0.9 Ex. 2 Ex. 15undrawn yarn of 130 1.30 150 20 2.8 24 0.9 6 1.0 Ex. 2 Ex. 16 undrawnyarn of 130 1.30 150 15 2.8 25 0.8 7 1.0 Ex. 8 Ex. 17 drawn yarn of 1401.05 — 35 2.8 45 1.0 6 1.0 Ex. 10 Com. Ex. drawn yarn of 110 1.50 — 203.0 25 0.4 25 2.1 15 Com. Ex. 3 Com. Ex. drawn yarn of 110 1.50 150 32.8 28 0.1 8 2.5 16 Com. Ex. 3 Com. Ex. yarn spun at 110 1.50 — 10 2.529 0.1 28 2.7 17 3000 m/min1 H: First heater temperature,2 H: Second heater temperatureDraw ratio: The ratio of peripheral speed of the drawing roller to thatof the feed rollerSW: Boiling water shrinkage

TABLE 5 Creep 3₁ Strength Strength rate at 1 HR Draw 2 HR Ratio 3₁ at25° C. Elongation at 90° C. 90° C. SW (° C.) ratio E (° C.) (%) CrystalU % (%) (cN/dtex) at 25° C. (%) (cN/dtex) (%) (%) Ex. 19 90 1.44 0.43130 13 no 1.0 4.3 24 1.5 9 4 (1.01+E) Ex. 20 90 1.44 0.43 130 12 no 1.04.2 22 1.5 9 4 (1.01+E) Ex. 21 90 1.44 0.43 130 14 no 1,2 4.1 22 1.5 9 4(1.01+E)1 HR: First hot roller temperature,2 HR: Second hot roller temperatureDraw ratio: The ratio of peripheral speed of the second hot roller tothat of the first hot rollerE: [Elongation (%) of undrawn yarn]/1003₁ Ratio (%): The ratio of 3₁ helical structure to the total fiber asdetermined by solid-state NMR3₁ Crystal: The presence of a crystal of the 3₁ helical structure asdetermined by WAXDSW: Boiling water shrinkage

1-25. (canceled)
 26. A process for producing a poly(lactic acid) fiber,the process comprising the step of drawing a poly(lactic acid) undrawnyarn at such a drawn ratio (DR) as to satisfy the following condition:0.85+(EL/100)≦DR≦2.0+(EL/100) wherein EL is the elongation (%) of theundrawn yarn.
 27. The process according to claim 26 wherein thepoly(lactic acid) undrawn yarn has a crystalline size in the (200) planeof equal to or more than 6 nm and is drawn at a temperature of equal toor higher than 85° C.
 28. The process according to claim 26 wherein thepoly(lactic acid) undrawn yarn has been obtained at a spinning speed ofequal to or more than 4000 m/min.
 29. The process according to claim 26wherein the poly(lactic acid) undrawn yarn has a crystalline size in the(200) plane of less than 6 nm and is drawn at a temperature of equal toor higher than 110° C.
 30. The process according to claim 26, furthercomprising the step of subjecting the drawn yarn to heat treatment at atemperature of equal to or higher than 120° C.
 31. The process accordingto claim 26 wherein the poly(lactic acid) undrawn yarn has Usterunevenness of less than or equal to 1.5%.
 32. The process according toclaim 26 wherein the drawing step is performed in a single stage. 33.(canceled)
 34. A process for producing a poly(lactic acid) crimped yarn,the process comprising the step of crimping a poly(lactic acid) fiberobtained by the process as claimed in any one of claims 26 to
 32. 35. Afibrous article at least partially comprising the poly(lactic acid)fiber obtained by the process as claimed in claim
 26. 36. (canceled) 37.A fibrous article at least partially comprising the poly(lactic acid)crimped yarn obtained by the process as claim in claim 34.